Tracing at least parts of an already existing image is an important aspect of the many drawing and reproduction fields. It is a means of reproducing images for drafting purposes, fine arts, and the like, allowing an image or parts thereof to be transferred from one medium to another, for instance from a photograph to paper or canvas.
Many techniques of tracing are known. Exemplitive thereof is the technique of placing paper or some other medium of sufficient transparency directly over an image, allowing the lines of the image to be seen through the transparency and thus allowing direct tracing of the image onto the transparency. This technique only permits reproduction of the image as it appears on the medium below the transparency, precluding even image scale variations.
Another example is an apparatus that optically projects an image onto a drawing medium from above. With such apparatus, the image projected usually can be varied as to scale at the drawing medium by changing the distance between the projecting means and the drawing medium and, to a limited extent, by the use of specialized lenses.
Since working surfaces are normally used disposed horizontally or at an incline from the horizontal, up to an angle approaching the vertical, such drawing tables with overhead image projectors present at least two significant disadvantages. First, even if the working surface is horizontal, and the image projection is strictly along the vertical, there will be interference with the optically-projected image cast onto the drawing medium from the body of the worker and/or his drawing instruments when, for example, his hand and pencil move into the path of the projection to perform the tracing. If the working surface is elevated to an inclined position, the image projection, in order to impinge along the normal, would need to be slanted, causing an even greater degree of interference by the body of a normally erect standing or sitting worker and his instruments. Thus vertical projection onto a horizontal working surface minimizes but does not remove the incidences of body interference, which of course includes interference by drawing instruments being used.
Second, most drawing environments, such as offices, work shops, and the like, are limited in the vertical space available above the working area. Hence, image scale variation dependent on the distance between the projection means and working surface is correspondingly limited. Moreover, elevation of a projection means from a position near the working surface to one a significant distance vertically therefrom would require apparatus of greater sophistication and higher cost than that normally associated with drawing table, such as drafting tables and the like.
Thus minimizing body interference requires the line of optical projection to be along the vertical, and having the line of optical projection along the vertical limits the range of scale variation by the change of the distance between the projection means and the working surface to the vertical space available and the type of practical apparatus available.
Moreover, none of the above described tracing techniques and means provide controlled distortion of the image being reproduced other than image scale variations.
Further, the field commonly known as computer graphics permits the storage, reproduction, and alteration of graphic data by means of a graphic data computer input mens, usually an electronically sensitized tablet or digitizer, on which a design, or lines or points defining the same, is drawn with a stylus. The graphic data is thus fed to a computer which can reproduce the same on a computer graphic display means, such as a television screen, or on a print-out sheet. Alterations in the graphic data can be directed by use of the same tablet. Regardless of whether the image is being for the first instance committed to the computer storage bank or reproduced directly on a graphic display means, the image must first be created or drawn on the tablet. It is to be understood herein that the term "draw" and variations thereof means not only the creation of a visable image by transfer of some tangible material from an instrument to the reproduction medium, such as the transfer of ink from a pen to paper, but also electronic transfer generated by the use of an appropriate instrument, such as a stylus, on an electronically sensitized tablet, or other computer input means, whereby the image so created is capable of being reproduced visually, although no visual reproduction is seen at the site of the computer input means, and similar transfers.
It would be desirable to provide a drawing table with means for projecting an optical image upon the working surface that is not disturbed by the body or instruments of the worker and which permits controlled distortion of the image being reproduced. It would be desirable to provide such a drawing table that is also selectively functional as a light table, i.e., a table whose working surface is illuminated from behind to improve visual display of transparencies or the like when supported on or held close to the working surface. It would be further desirable to provide such a table wherein the working surface can be positioned at a plurality of angles from the horizontal, and wherein the illumination, when selected, can be easily varied as desired.
It would also be desirable to provide a drawing table wherein image scale variations dependent upon the length of the line of projection can be substantially determined by changing the distance between the working surface and the projecting means substantially along the horizontal. It would also be desirable to provide such a drawing table wherein the image projected onto the working surface could be distorted in modes other than image scale variations.
It would also be desirable to provide at least some of the advantages in reproduction and tracing techniques and means enumerated above to the field of computer graphics and further to provide means for overlaying a computer graphics input means with its display means for greater precision in making alterations on graphic data already held by the computer.
It would be desirable to provide a drawing table having one or more of the above enumerated advantages which additionally is easily portable.